<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        html,body{
            padding:0;
            margin:0;
            height:100%;
            width:100%;
        }
       .bs-main{
           width:100%;
           height:100%;
           background:url("/img/pic.png") no-repeat center center;
           background-size:500px 500px;
       }
    </style>
</head>
<body>
<div class="bs-main">

</div>

</body>
</html>